There is a large body of evidence linking zinc deficiency and pneumonia. Zinc is an essential nutrient for both humans and bacterial pathogens, but up to one third of the world population does not consume sufficient dietary zinc. The World Health Organization has estimated that zinc deficiency contributes to up to 16% of all lower respiratory globally, and a pooled analysis of randomized studies found that zinc supplementation reduced pneumonia incidence by 41%. Zinc is important for regulating the immune system, partly through direct sensing of intracellular zinc levels by immunoregulators. Additionally, the host immune protein calprotectin sequesters zinc from bacterial pathogens, suppressing their growth and dissemination. In the United States, certain populations are at increased risk for zinc deficiency and infection by the opportunistic pathogen Acinetobacter baumannii. Because zinc acquisition is critical to A. baumannii during pneumonia pathogenesis, we reasoned that it could serve as a model for defining the molecular mechanisms by which zinc deficiency increases pneumonia susceptibility. Preliminary data from our laboratory demonstrated that zinc deficiency significantly increases mortality from A. baumannii pneumonia by 24 hours post infection. The central hypothesis of this proposal is that mortality caused by A. baumannii pneumonia in zinc deficient mice is due to altered zinc homeostasis, which causes dysregulation of the innate immune response and enhanced bacterial virulence. The experiments proposed will integrate in vitro and in vivo studies linking zinc deficiency and inflammation caused by A. baumannii infection. In Specific Aim 1, human lung epithelial cells will be analyzed for differential responses to A. baumannii exposure based on zinc status using an innovative and high throughput mass spectrometry assay platform. Specific Aim 2 will determine the effect of zinc nutritional status on A. baumannii pneumonia by elemental and immunological analysis of the host. In Specific Aim 3, we propose to identify bacterial genes important for the observed enhanced mortality using a high throughput transposon sequencing strategy. This integrated approach will define molecular links between zinc deficiency and pneumonia and has the potential to significantly impact our understanding of nutritional determinants of infectious disease.